Lodore Formation
The Cambrian quartzitic sandstone of the Gates of Lodore — the first sea over the Uinta basement, resting on the Great Unconformity.
Also known as: Lodore, Lodore Shale
Cambrian — the first great burst of sea life
The world back then
Late Cambrian, roughly 500 million years ago. The very first sea is washing over an ancient, long-bare basement, dropping a thin layer of white-and-red sand at the Gates of Lodore — the leading edge of the ocean creeping across a lifeless continent. Shallow, quiet, and new. Above it, hundreds of millions of years of rock will simply never get deposited.
You float in through that same Gates of Lodore today, waved straight into the heart of the range, doing nothing to earn it. That first sea took a half-billion years to feel its way in; you get a permit and a push-off. There's a deep luck in being the warm, curious creature who arrives long after the door was opened and just drifts through.
Recognize it in the field
- Typical color
- white to red
- Weathers as
- Ledge- and cliff-forming quartzose sandstone — the lower walls of the Gates of Lodore.
- Grain
- coarse, moderately-to-well sorted, subrounded; quartzitic to arkosic
Look for
- white-to-red quartzitic and arkosic sandstone
- silty shale interbeds
- rests on the Uinta Mountain Group across the Great Unconformity
- the namesake of the Gates of Lodore
How this rock was made
A thin sandstone deposited in a shallow marine trough as the Cambrian sea transgressed over the Precambrian basement.
The setting: rising-sea (transgressive) shallow-marine (the basal Paleozoic transgression)
~350-465 ft regionally.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Uinta Mountains (Middle Rocky Mountains province; NPS files Dinosaur NM under Colorado Plateaus)
- Lodore Canyon / Gates of Lodore (Green River, Dinosaur NM)
Float past it: Lodore Canyon · Whirlpool Canyon